Patent GB-920022-A (GB)
Title: Lockout circuit for electrowriter transmitter
IPC: G08C21/00
Filed: 1961-08-09
Abstract: 920,022. Writing telegraph " lock out " systems. VICTOR COMPTOMETER CORPORATION. Aug. 9, 1961 [Sept. 12, 1960], No. 28747/61. Class 40 (1). General operation.-A lock out amplifier sensitive to transmitted signals, prevents a writing telegraph transmitting station using modulated signals from sending when another transmitter is already working the receiver to which it is intended to transmit, further provision being made to prevent its operating in response to signals developed by its own transmitter. In Fig. 2 a tuned look-out amplifier 61 responsive to signals from a transmitter feeding a common line 18 prevents its own transmitter 11 from transmitting by the operation of a pen orientation sensitive switch 32 and two control relays 88, 112 which prevent oscillator gates 51, 52 from conducting. The lock-out amplifier is muted so as to prevent its response to signals sent out by its own transmitter by the interlocking of relays 88, 112 controlling the emitter connection of the second amplifier stage. Detail arrangements.-In Fig. 1 transmitting stations 11A, 11B comprise a pen 15 having a stylus control member 17 and a support arm 16 controlling the electrical translation, the stations being coupled over a common transmission line 18 to receiving stations 12c, 12d responsive to frequency-modulated signals. Fig. 2 shows an operating circuit of either transmitters and includes a pen 15 embodying a recording medium contact sensing switch 31 and an orientation sensitive switch 32 responsive to the inclination of the pen from the horizontal. A pen linkage mechanism 33 is connected to a pair of position transformers 34, 35 which each include respectively a fixed core 36, 37, an input winding 38, 39, an output winding 40, 41, a pen linked core 42, 43, movable relatively to the main core 36, 37, and carrying a winding 44, 45. The transmitter circuit includes " X " and " Y " oscillators 47 and 48 respectively associated with winding 39 through a normally closed gate 51 and a winding 38 through a similar gate 52. Windings 43, 44 are coupled back to their respective " X " and " Y " oscillators. Movement of the pen 15 in the " X " co - ordinate direction causes changes in the position of the movable core 43 relatively to the core 37 and modulation of the oscillator output frequency. Similar modulation of the " Y " oscillator is caused by pen movement in the " Y " coordinate direction. A lock-out amplifier 61 is coupled to the transmission line 18 by a tuned transformer circuit 62, 65 being preferably responsive to the " Y " oscillator centre frequency. To energize the transmitter, control switch 129 is closed, but this by itself is insufficient to complete a circuit between a negative supply C and the gates 51, 52, thus " opening " them, as contacts 113, 115 of a control relay 112 are open, this relay being itself operated by a " lock-out " amplifier controlled relay 88. With switch 129 closed, the gates will, however, be made conductive by the relay 112, which will be actuated automatically by the closure of the pen-mounted switch 32. The coil 111 will then be connected to the supply C and through contaets 103, 104 of relay 88 and the switch 32 to ground, thus closing the contacts 113, 115 and gate circuits 51, 52 to conduct and signals from the oscillators to their transformers. In addition contacts 117, 119 of relay 112 close and energize a " send " lamp 121. As long as the switch 129 is closed and the position-actuated switch 32 is operated, the " send " lamp 121 will be lit. Each time the contact-sensitive switch 31 is closed the operating coil 124 of relay 123 is energized and closes contacts 125, 127, thus lighting a " busy " lamp 108 and a pen contact signal generator 53 which causes a small change in the oscillator frequency. Where an incoming signal is already present on the line 18 from another transmitter, the signal will excite the amplifier tuned input circuit and is amplified to energize a " look-out " relay 88, thus closing contacts 101, 104 and 105, 107 thereby preventing the operation of the relay 112 due to the opening of contact 104. The closure of switch 32 will therefore be ineffective in completing the relay 112 circuit and hence the gates 51, 52 will remain closed and transmission impossible. The " busy " lamp 108 will be continuously lit due to contacts 105, 107 on relay 88. When the transmitter 11 is to be operated, the relay 112 is energized as previously described and contacts 113, 115 open the earth return of the amplifier transistor 82, thus rendering this "cut-off" and preventing the relay 88 from being energized. The transmitter can thus not be " locked out " by its own signals but as soon as the switch 32 is open due to the operator putting down the pen 15, relay 112 is de-energized and if another transmitter now comes on the line, the lock-out system will respond.